A power supply circuit of the present invention includes a voltage boosting capacitor, a first switch, a second switch, an addition comparison circuit, and a control circuit. The first switch charges the voltage boosting capacitor by applying a first voltage thereto. The second switch connects a second voltage serially to the voltage boosting capacitor that is already charged, thereby boosting the voltage therein. The addition comparison circuit adds up the voltage of the voltage boosting capacitor and the second voltage and compares the comparison result, with a predetermined threshold value. The control circuit controls the on/off state of the first switch according to the comparison result of the addition comparison circuit.